A telescoping torque tube is a type of shaft used in drive lines that can be temporarily shortened in length by moving an end fitting on the torque tube from an extended position to a retracted position to facilitate installation or removal of the torque tube. In order for the torque tube to function properly, the telescoping end fitting must be locked in the extended position. Torque is commonly transmitted between the torque tube and end fitting by meshed splines on the torque tube and end fitting.
There are several known ways of releasably locking an end fitting at an extended position on a torque tube. One technique simply uses a cross bolt to lock the end fitting to the torque tube. The installer inserts the cross bolt transversely through aligned holes in axially overlapping end portions of the end fitting and the torque tube and uses the required tools to tighten the bolt. Typically, the cross bolt only restrains axial motion of the end fitting, and torque is transmitted by meshed splines, unless the torque carried by the torque tube is very low. The cross bolt must be removed to shorten the telescoping assembly.
Another technique uses an axially arranged internal spring acting between the torque tube and the end fitting to bias the end fitting toward the extended position. The end fitting and torque tube may be configured such that the end fitting can be locked in the extended and retracted positions by relative rotation between the end fitting and the torque tube about a longitudinal axis of the torque tube, and can be unlocked by relative counter-rotation. To shorten the telescoping torque tube assembly, the installer may rotate the end fitting to unlock it from the extended position, and then push the end fitting to the retracted position.
Another known technique employs a spring-loaded radially extending detent pin arranged to lock the end fitting of a telescoping torque tube assembly from axial movement. The installer presses the spring detent pin to stop the interference between the pin and the end fitting and allows axial movement of the end fitting.
These state of the art approaches for coupling an end fitting to a torque tube in a telescoping torque tube assembly require additional parts beyond the torque tube and end fitting, thereby adding weight and cost to the assembly while diminishing its reliability. The procedure to retract the end fitting may be time consuming, may require tools, and may involve loose fasteners.